Congestive heart failure (CHF) is a condition that is often associated with a weakened heart that cannot pump enough blood to body organs. For example, as pumping action is lost, blood may back up into the heart and other areas of the body, including the liver, gastrointestinal tract, extremities and/or lungs. While implantable cardiac therapy devices are often used to overcome deleterious effects caused by CHF, such devices cannot halt progress of CHF. However, some implantable cardiac devices can be programmed to compensate for worsening stages of CHF. For example, as CHF progresses, the myocardium weakens, which typically results in an increased left ventricular volume. To compensate for the increase in volume, a clinician may periodically measure a patient's left ventricular diameter, or another parameter associated with cardiac geometry, and program the implanted cardiac therapy device accordingly. This technique, however, requires clinical intervention, which consumes time and resources. Reliable exemplary devices, methods and/or systems for determining cardiac geometry using an implanted cardiac therapy device optionally overcome such limitations and are presented herein.